With the old magnetic stud finder there was a problem because it found nails not studs. The magnet did stud finding by the nails that held lath strips or rock-lath to the studs. Or if the plaster on the wall is not too thick, the magnetic stud finder could find the nails that secured the studs at the top or the base of the wall.
Eventually the magnetic stud finder will find some nails, it just takes patience and not moving the stud finder too quickly. Once you think you have found a stud, check 16-inches to the right or the left for another. With minor exceptions, most studs in even the oldest homes built in this century are on 16-inch centers.
Another way to shorten the search isto check for studs near receptacles and heat vents. They are attached to a stud; you just have to find out which side of the stud they are nailed to. I will pull off an electrical cover plate and tap a small nail at a sharp angle to the right and the left of the box to check for the stud. Sometimes the box has brackets that hold it about an inch away from the stud so don’t let that fool you, you will just need a longer nail. Do not drive the nail inside of the box or you could get shocked.
Windows and doorways are random in a wall and usually do not indicate where the next stud will be. Most window and door openings have at least two studs on either side that provide material to attach curtains or moldings. Measuring 16-inches from a corner will usually not indicate the next stud because the layout of a stud wall starts at the very exterior of a structure.
Sometimes your project will not fall on a stud. These days there are tons of excellent fasteners that hold over 100 pounds. One of the best fasteners for this situation is an anchor called a TOGGLER. It is similar to the old toggle bolt but with a zip tie holder. This way you can install the fasteners before hand and use a machine screw to hang your project.
It happens that you want to hang a cabinet in the bathroom but I have been unsuccessful at finding a stud. It may cost you $20 dollars on an electronic stud finder.